Comparing lumbar spinal muscles activity in scoliotic and healthy subjects using finite element method

Many spinal problems which could lead to pain are associated with the instability of spine. Experiments have shown that the ligamentous spine is inherently unstable, because the isolated lumbar spine buckles under approximately 90N load. Spinal deformities can originate instability of spine, but studies have shown that in normal state, combination of the various mechanisms, such as muscle forces and intra-abdominal pressure render the spine stable. In this research, we try to find out the relationship between spinal deformity and lumbar muscles activity. According to the biomechanical and geometrical complexity of the spine, it’s crucial to use biomechanical models in order to study the stability of the spine. Granata and Wilson presented a simple two-links model of lumbar spine considering twelve muscles, and by satisfying the mechanical stability conditions, they calculated the muscular forces for different physical activities. Through experiments conducted using Electromyography (EMG), activity of the trunk muscles were recorded and compared with the predicted model results. In this paper, Granata analytical model is verified using a finite element model. Muscular forces are calculated subject to satisfying the spinal stability conditions for a standing Granata analytical model, and they are compared with the numerical results. Subsequently, a similar model is adapted to the subjects with scoliosis, and spinal stability conditions in these models are compared with healthy one. Then the relationship between progression of spinal deformities and lumbar muscles activities is illustrated. Finally contribution of spinal deformities on the stability of spine is studied. In the more complex physical activities such as load lifting and bending, it is inconvenient to use analytical methods, contrarily the finite element method is a more appropriate tool to study the stability of the spine.